1. Field of the Invention
The present invention relates to phosphors.
2. Description of the Related Art
To date, a variety of red phosphors have been developed. For example, a red phosphor with a composition of CaAlSiN3:Eu, (Ca,Sr)AlSiN3:Eu, or Ca2Si5N8:Eu has been developed (JP3837588, JP2008-106224, JP2005-093912).
However, conventional red phosphors, including the phosphors with the aforementioned compositions, are mainly nitride phosphors. Synthesizing nitride phosphors requires a specific environment, such as a deoxidized atmosphere or a high-temperature and high-pressure environment, which leads to an increase in the manufacturing cost.
The edge of the excitation spectrum of the just-discussed red phosphors is in a range of 500 to 550 nm. This means that when, in order to realize white light, this sort of red phosphor is used together with a phosphor that emits light in another color, the red phosphor ends up absorbing the light that the blue, green, yellow, or other color phosphor emits, and converts the other color to red. As a consequence, in response to subtle fluctuations in the compositional content of the phosphor or the manner in which it is coated on, large deviation in chromaticity from that of a desired emission color can occur, making adjustment of the color challenging.